1. Technical Field
This invention relates generally to a field effect mode electro-optical device, such as a twisted nematic liquid crystal device, and more particularly to a field effect mode electro-optical device having photospacers that are arranged in an a quasi-random arrangement so as to minimize optical interference with other optical components in a system.
2. Background Art
Copending, commonly assigned U.S. application Ser. No. 11/684,454, entitled “Multimodal Adaptive User Interface for a Portable Electronic Device,” teaches a multimodal electronic device that employs a segmented optical shutter enabled dynamic keypad. The segmented optical shutter, which in one embodiment is a twisted nematic liquid crystal display, is used for presenting one of a plurality of keypad configurations to a user. Electric fields are applied to the segmented optical shutter, thereby changing the optical properties of the segments of the optical shutter to hide and reveal various user actuation targets. Additionally, a high-resolution display can be hidden from the user when the device is OFF, yet revealed when the device is ON. The application of the electric field causes the polarity of light passing through the optical shutter to rotate, thereby opening or closing segments or windows.
While this invention works well in practice, in some configurations the physical properties of the high-resolution display being used can cause optical interference that is visible to a user. For instance, where the segmented optical shutter is used to hide and reveal the high-resolution display, which can be a pixilated liquid crystal display, the optical shutter is disposed atop the high-resolution display. Liquid crystal displays are thin-film transistor devices and include an inherent “black matrix” that is formed by the opaque boundaries of each pixel. While these boundaries are not visible at a distance, they can be seen upon close examination. Further, non-optical elements such as capacitors, electrical traces, and semiconductor materials may also form small, opaque patterns or regions.
Some optical shutter devices use photolithographically deposited spacers (“photospacers”), spread apart in equal periodic patterns, rows, or columns to keep the substrates of the optical shutter from touching. When the photospacers of the optical shutter sufficiently coincide with the opaque regions or black matrix of the pixilated liquid crystal device, optical interference can occur. In some cases a moiré pattern may appear to the user. While this condition happens infrequently and only when certain, somewhat unlikely conditions occur simultaneously, when it does occur, it can be distracting to a user.
There is thus a need for an improved optical shutter device that reduces optical interference with other system components when used in an optical system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.